package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

/**
 * @author wangcw
 */
public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;
    private SimpleExecutor simpleExecutor;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
        this.simpleExecutor = new SimpleExecutor();
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {
        //将要去完成对simpleExecutor里的query方法的调用
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if(objects.size()==1){
            return (T) objects.get(0);
        }else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public void insert(String statementid, Object... params) throws Exception {
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        simpleExecutor.insert(configuration, mappedStatement, params);
    }

    @Override
    public Integer update(String statementid, Object... params) throws Exception {
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public Integer delete(String statementid, Object... params) throws Exception {
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        return simpleExecutor.delete(configuration, mappedStatement, params);
    }


    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass},
                new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                // 底层都还是去执行JDBC代码 //根据不同情况，来调用selectList或者selectOne
                // 准备参数 1：statementId :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                // 方法名：findAll
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String statementId = className+"."+methodName;
                // 准备参数2：params:args
                // 获取被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();
                // 判断是否进行了 泛型类型参数化
                return choiceProcess(genericReturnType,statementId,args);
            }
        });

        return (T) proxyInstance;
    }


    /**
     * 选择需要执行的操作
     * @param genericReturnType
     * @param statementId
     * @param args
     * @return
     * @throws Exception
     */
    private Object choiceProcess(Type genericReturnType,String statementId,Object... args) throws Exception {
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        switch (mappedStatement.getProcessType()){
            case insert:
                insert(statementId,args);
                return null;
            case delete:
                return delete(statementId,args);
            case update:
                return update(statementId,args);
            case select:
                if(genericReturnType instanceof ParameterizedType){
                    List<Object> objects = selectList(statementId, args);
                    return objects;
                }
                return selectOne(statementId,args);
            default:

                break;
        }
        return null;
    }

}
